Case report: guanfacine overdose

July 17, 2014, 7:52 pm

Intuniv (Guanfacine)

Intuniv (Guanfacine)


Prolonged Bradycardia and Hypotension Following Guanfacine Extended Release Overdose. Walton J et al. J Child Adolesc Psychopharmacol 2014 Jul 10 [Epub ahead of print]


Guanfacine is a central α2-agonist with a mechanism of action similar to that of clonidine. Originally marketed as an antihypertensive agent, it is now available as an extended-release preparation (Imtuniv) for treating children ages 6-17 with attention-deficit hyperactivity disorder (ADHD). It is thought the mechanism of action in that condition may involve stimulation of α2-receptors in the prefrontal cortex.

As with clonidine, guanfacine can cause initial hypertension (from peripheral α-agonist activity) followed by prolonged bradycardia and hypotension (from central α2 effects.

This short case report describes a 9-year-old boy with ADHD who was taking dexmethylphenidate and risperidone, as well as extended-release guanfacine (3 mg in the morning.) Inadvertently, the child received an extra dose of guanfacine-ER at around noon. Four hours later he was lethargic and drowsy but arousable. On arrival at hospital, he was bradycardic (40-50 bpm) and hypotensive (~80/40 mm Hg.) He was admitted for observation and given IV fluids. He recovered uneventfully over the next 24 hours.

In their discussions, the authors suggest that — as illustrated by their case — a prolonged hypotensive response can follow even a mild overdose of guanfacine, and any overdose of this agent should mandate medical evaluation.

To read my Emergency Medicine News column discussing the toxicology of newer ADHD drugs, click here.


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